In his videos he shows step by step how to root, flash custom ROMs, make nandroid backups, and many other topics. Read everything you can in the root thread and watch his videos... they're very good.

Yes there is a way to "unroot" (there's a video on how to do that above) and go back to complete factory stock just like the phone comes. Program for that is called Odin.

I have my phone rooted, and am running a custom ROM... it made my phone a lot faster, more efficient, and improved battery life. I def recommend looking into it and getting all the facts, and decide if its right for you.